The present invention relates to diodes, and more particularly to diodes having a buried lateral construction suitable for integrated circuits.
An impact-avalanche-and-transit-time (IMPATT) diode is a desirable component for use as a generator of microwave frequency radiation due to its simplicity. However, its input resistance is low compared to a standard 50 ohm transmission line at these frequencies and its input capacitance is relatively high, resulting in restricted bandwidth. A solution to these problems would be to couple several such diodes in series in order to raise the input resistance and lower the input capacitance. However, such a diode is usually formed in a vertical (perpendicular to a substrate) configuration, which makes a series connection impractical due to the difficulty of making a connection from the bottom electrode of one diode to the top electrode of another diode when the diodes are made in integrated circuit (IC) form. U.S. Pat. No. 3,981,073 discloses a lateral semiconductor Gunn device adjacent an oxide and expressly suggests a similar construction for an IMPATT diode in the penultimate paragraph of the detailed description thereof. However, while a Gunn device has only regions of a single conductivity type with an applied electric field distributed across all the regions, an IMPATT diode has a P-N junction having a high electric field thereacross. This can result in voltage breakdown of the IMPATT diode due to crystal defects at the oxide-semiconductor interface before the critical field necessary for oscillation is achieved. Further, carriers can become trapped in the oxide and surface states of the semiconductor, which reduces the efficiency of the diode since trapped carriers, even if remitted, will usually be out of phase with the avalanche current.
It is, therefore, desirable to have a diode that can be made in IC form that can be readily series coupled with other such diodes and which resists voltage breakdown and loss of efficiency.